THE LUTEINIZING HORMONE RECEPTOR

Abstract

▪ Abstract The luteinizing hormone receptor (LHR) is a member of the subfamily of glycoprotein hormone receptors within the superfamily of G protein–coupled receptor (GPCR)/seven-transmembrane domain receptors. Over the past eight years, major advances have been made in determining the structure and function of the LHR and its gene. The hormone-binding domain has been localized to exons 1–7 in the extracellular (EC) domain/region of the receptor, which contains several leucine-rich repeats. High-affinity binding of LH and human chorionic gonadotropin (hCG) causes secondary hormone or receptor contacts to be established with regions of the EC loop/transmembrane module that initiate signal transduction. Models of hormone-receptor interaction have been derived from the crystal structures of hCG and of the ribonuclease inhibitor, which also contains leucine-rich repeats. Such models provide a framework for the interpretation of mutational studies and for further experiments. The extracellular domain of the receptor has been overexpressed in vitro, which will facilitate crystallographic resolution of the structure of the receptor-binding site. The transmembrane domain/loop/cytoplasmic module transduces the signal for couplingto G proteins. Several constitutive, activating mutations that cause human disease have been found in helix VI and adjacent structures. These mutations have provided valuable information about mechanisms of signal transfer and G protein coupling. The structure of the LHR gene has been elucidated, and the regulation of its transcription is beginning to be understood. Valuable insights into receptor evolution have been derived from analysis of sequence homologies, the gene structure of glycoprotein hormone receptors and other members of the GPCR family, and the glycoprotein hormone receptor–like precursors identified in several invertebrate species.